2020 CIME II Problems/Problem 12

Note that the $\text{lcm}(\text{gcd}(a,b),c)$ and its iterations are all divisible by 180. This implies that 2 of $a,b,c$ are divisible by 4, 2 are divisible by 9 and 2 are divisible by 5. \[a,b,c = d 20, e 36, f 45\]

Next we note that iterations are 180,$2\times 180$,$3 \times 180$. This implies that $d$ or $e$ must have an additional factor of 2 and $e$ or $f$ must have an additional factor of 3. The sum is minimized if d=2 and e=3 and f=1.

\[a,b,c = 40,45,108\] \[a+b+c = 193\]

Invalid username
Login to AoPS